1. Field of the Invention
The present invention relates to an apparatus for controlling a fuel injection quantity supplied to an engine, and in particular for making a load correction of the fuel injection quantity at a transient time.
2. Description of the Related Art
An air fuel ratio differs between normal and transient driving conditions due to a fact that mutual relation between a quantity of fuel deposited on the inner wall of an intake manifold and an evaporation quantity of fuel deposited thereon varies. In order to prevent this deviation of the air fuel ratio, an apparatus for controlling a fuel injection quantity for an internal combustion engine has been proposed which corrects a reference fuel injection quantity set based on a quantity of intake air sucked into an internal combustion engine by using a transient correction value to be set in response to each transient condition of the engine (for example, JP-B-64-6333).
In a mass flow type apparatus for controlling a quantity of fuel injection into an internal combustion engine, an intake air quantity is detected by means of an air flow meter and the like and a reference fuel injection quantity is set depending upon the detected intake air quantity. With such a type of apparatus, the reference fuel injection quantity becomes excessive, because air density decreases at a higher altitude place as compared with a lower altitude place. In order to prevent such a deviation of an air fuel ratio, an atmosphere correction system for decreasing the reference fuel injection quantity with a decrease in the atmospheric pressure has been proposed.
In a speed density type system for controlling a fuel injection quantity of an internal combustion engine, intake air pressure in an intake pipe downstream of a throttle valve is detected by using a pressure sensor and thereby an intake air quantity is determined indirectly from the detected intake pipe pressure, and then a reference fuel injection quantity is set depending upon the determined intake air quantity. With such a speed density type system, since atmospheric pressure becomes lower at a higher altitude place as compared with a lower altitude place and accordingly the intake air quantity is increased at a higher altitude place even with the same intake pipe pressure, the reference fuel injection quantity becomes too small at a higher altitude place. In order to prevent such a deviation of an air fuel ratio, an atmosphere correction system, which increases and corrects the reference fuel injection quantity with a decrease in atmospheric pressure, has been proposed.
According to the inventors' experiments using various internal combustion engines, it has been found that the above-mentioned mutual relation between the deposition and evaporation of fuel in an intake manifold varies depending not only on a transient condition but also on atmospheric pressure. More precisely, it has been found that a quantity of fuel deposited on an intake manifold decreases with a decrease in atmospheric pressure even under the same transient condition. Therefore, there is a problem that air fuel mixture becomes richer so that exhaust emission is deteriorated under lower atmospheric pressure, if a reference fuel injection quantity is corrected with a transient correction value set based only on transient conditions, as is done in the above mentioned apparatuses.
Further, the atmosphere correction in the fuel injection quantity control apparatuses for an internal combustion engine of the mass flow type and of the speed density type aims to correct an error of a detected intake air quantity. Even with such atmosphere correction, it is not possible to correct the deviation of an air fuel ratio due to the fact that the mutual relation between the deposition and evaporation of fuel in an intake manifold varies also with a change of atmospheric pressure, even if such an atmosphere correction is carried out.